ide-tape: remove pipeline-specific members from struct ide_tape_obj

Bart:
- merge "ide-tape: remove pipeline-specific code from idetape_setup" patch
- cleanup __idetape_discard_read_pipeline()
- cleanup idetape_empty_write_pipeline()
- fix 't' assignment in idetape_setup()
- fix idetape_blkdev_ioctl() w.r.t. 'nr_stages'

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>